Bottom Line:
These compounds also inhibit CDK9 which is relevant for MCL-1 expression.The activity and mechanism of action of the dual CDC7/CDK9 inhibitor PHA-767491 was assessed in a panel of multiple myeloma cell lines, in primary samples from patients, in the presence of stromal cells and in combination with drugs used in current chemotherapeutic regimens.We report that in all conditions myeloma cells undergo cell death upon PHA-767491 treatment and we report an overall additive effect with melphalan, bortezomib and doxorubicin, thus supporting further assessment of targeting CDC7 and CDK9 in multiple myeloma.

Affiliation: Centre for Chromosome Biology, School of Natural Sciences National University of Ireland Galway, Galway, Ireland. michael.odwyer@nuigalway.ie.

ABSTRACTTwo key features of myeloma cells are the deregulation of the cell cycle and the dependency on the expression of the BCL2 family of anti-apoptotic proteins. The cell division cycle 7 (CDC7) is an essential S-phase kinase and emerging CDC7 inhibitors are effective in a variety of preclinical cancer models. These compounds also inhibit CDK9 which is relevant for MCL-1 expression. The activity and mechanism of action of the dual CDC7/CDK9 inhibitor PHA-767491 was assessed in a panel of multiple myeloma cell lines, in primary samples from patients, in the presence of stromal cells and in combination with drugs used in current chemotherapeutic regimens. We report that in all conditions myeloma cells undergo cell death upon PHA-767491 treatment and we report an overall additive effect with melphalan, bortezomib and doxorubicin, thus supporting further assessment of targeting CDC7 and CDK9 in multiple myeloma.

cancers-05-00901-f008: Sequential combination analysis of PHA-767491 with drugs constituting standard of care. MM1S cells were treated with Melphalan (Range 2 to 32 µM, A) Doxorubicin (Range 31 to 500 nM, B) Bortezomib (Range 1.3 to 20 nM, C) for 3 h followed by treatment with PHA-767491 in a non-constant ratio. Cell viability was examined by CellTiter Glo 48 h after drug treatment. Combination indices (CI) were calculated and the Log CI (circles) plotted in relation to the fraction of cells affected (Fa) at any given experimental point.

Mentions:
In order to test the potential of a CDC7/CDK9 dual inhibitor in combination with standards of care, MM1S cells were treated with PHA-767491 together with melphalan, bortezomib, or doxorubicin. Combination experiments were performed by treating cells with each drug in constant and non-constant combination ratios. After incubation, cell viability was assessed and data was then analyzed with the Chou-Talalay median-dose-effect formula. The combination index (CI) for each experimental combination point was calculated [39]. In the first set of experiments, drugs were administered simultaneously. We observed that almost all CI calculated were either equal or very similar to 1 (Figure 6). Similarly, when the drugs were combined in a sequential manner with either melphalan, bortezomib or doxorubicin administered 3 h before or after PHA-767491, the calculated CI was still very close to 1 (Supplementary Figure S1 and Figure S2). Overall, these results indicate a general additive cytotoxic effect of PHA-767491 with each standard of care in the myeloma cell line used for these experiments.

cancers-05-00901-f008: Sequential combination analysis of PHA-767491 with drugs constituting standard of care. MM1S cells were treated with Melphalan (Range 2 to 32 µM, A) Doxorubicin (Range 31 to 500 nM, B) Bortezomib (Range 1.3 to 20 nM, C) for 3 h followed by treatment with PHA-767491 in a non-constant ratio. Cell viability was examined by CellTiter Glo 48 h after drug treatment. Combination indices (CI) were calculated and the Log CI (circles) plotted in relation to the fraction of cells affected (Fa) at any given experimental point.

Mentions:
In order to test the potential of a CDC7/CDK9 dual inhibitor in combination with standards of care, MM1S cells were treated with PHA-767491 together with melphalan, bortezomib, or doxorubicin. Combination experiments were performed by treating cells with each drug in constant and non-constant combination ratios. After incubation, cell viability was assessed and data was then analyzed with the Chou-Talalay median-dose-effect formula. The combination index (CI) for each experimental combination point was calculated [39]. In the first set of experiments, drugs were administered simultaneously. We observed that almost all CI calculated were either equal or very similar to 1 (Figure 6). Similarly, when the drugs were combined in a sequential manner with either melphalan, bortezomib or doxorubicin administered 3 h before or after PHA-767491, the calculated CI was still very close to 1 (Supplementary Figure S1 and Figure S2). Overall, these results indicate a general additive cytotoxic effect of PHA-767491 with each standard of care in the myeloma cell line used for these experiments.

Bottom Line:
These compounds also inhibit CDK9 which is relevant for MCL-1 expression.The activity and mechanism of action of the dual CDC7/CDK9 inhibitor PHA-767491 was assessed in a panel of multiple myeloma cell lines, in primary samples from patients, in the presence of stromal cells and in combination with drugs used in current chemotherapeutic regimens.We report that in all conditions myeloma cells undergo cell death upon PHA-767491 treatment and we report an overall additive effect with melphalan, bortezomib and doxorubicin, thus supporting further assessment of targeting CDC7 and CDK9 in multiple myeloma.

Affiliation:
Centre for Chromosome Biology, School of Natural Sciences National University of Ireland Galway, Galway, Ireland. michael.odwyer@nuigalway.ie.

ABSTRACTTwo key features of myeloma cells are the deregulation of the cell cycle and the dependency on the expression of the BCL2 family of anti-apoptotic proteins. The cell division cycle 7 (CDC7) is an essential S-phase kinase and emerging CDC7 inhibitors are effective in a variety of preclinical cancer models. These compounds also inhibit CDK9 which is relevant for MCL-1 expression. The activity and mechanism of action of the dual CDC7/CDK9 inhibitor PHA-767491 was assessed in a panel of multiple myeloma cell lines, in primary samples from patients, in the presence of stromal cells and in combination with drugs used in current chemotherapeutic regimens. We report that in all conditions myeloma cells undergo cell death upon PHA-767491 treatment and we report an overall additive effect with melphalan, bortezomib and doxorubicin, thus supporting further assessment of targeting CDC7 and CDK9 in multiple myeloma.